1. Technical Field
The present invention relates to a method for adjusting a light emitting device that can perform emission of pulsed light.
2. Background Art
In technology using laser light for measuring distances, various types of machining, etc., a short pulsed laser light with a pulse width of several tens to not more than several hundreds of picoseconds is desired. For example, in distance measurements using pulsed laser light, the precision of measuring distances can be improved by using pulsed light with a narrow pulse width. As a technique for generating laser light with a narrow pulse width, techniques disclosed in, for example, Japanese Examined Patent Application Publication No. 7-109911, Japanese Unexamined Patent Application Laid-Open No. 55-107282, and Japanese Unexamined Patent Application Laid-Open No. 2002-368329 are publicly known.
FIG. 1 shows a relationship between driving current and output light of a laser diode (LD). As shown in FIG. 1, when driving current is applied to the LD, a phenomenon may occur in which pulse-like light is emitted at first, the emitted light gradually decreases in the amplitude while oscillating, and light with a constant intensity is finally emitted. This phenomenon can be observed in typical laser diodes. The above oscillation in light intensity, which occurs in the initial stage of the light emission and gradually decreases, is called “relaxation oscillation”.
In order to perform emission of light with a short pulse width, a method of applying driving current for a short period and performing emission of only initial pulsed light, as shown in FIG. 2, may be used. However, it is difficult to generate a driving current having a time length on the order of several tens to several hundreds of picoseconds using a simple circuit.
For example, a sine wave and a square wave of a frequency of approximately 200 MHz are easily obtained by using commercial ICs. However, for example, considering that the cycle of a high frequency of 100 MHz is 10−8 seconds (10 nanoseconds=10,000 picoseconds), it is not easy to obtain pulse-like driving current having a time length on the order of several tens to several hundreds of picoseconds.
The pulse-like driving current having a time length on the order of several tens to several hundreds of picoseconds can be obtained by using a high frequency technique in the microwave band. For example, a signal of several tens of GHz can be obtained by an oscillator using a YIG resonator, and the pulse-like driving current having a time length on the order of several tens to several hundreds of picoseconds can be obtained by utilizing this technique. Nevertheless, the high frequency technique in the microwave band may not be suitable for use for, for example, outdoor measuring devices and the like, in view of circuit scale, production cost, need for complicated adjustment, and large consumption of electric power.